Fining of glass



Patented Sept. 28, 1943.

V UNITED STATES PATENT OFFICE FIN'ING or GLASS Frederick W. Adams,Pittsburgh, Pa., assignor to Pittsburgh Plate Glass Company, AlleghenyCounty, Pa., a corporation of Pennsylvania No Drawing.

1 Claim.

The present invention relates to the treatment of glass for purposes ofremoving water vapors and other gases therefrom.

An object of the invention is to provide a glass which is substantiallyfree of gas bubbles,-such as may be occasioned by carbon dioxide, airand Application February 25, 1942, Serial N 0. 432,269

" the melt, which has been treated'with carbon water vapors, which glassis also substantiallyi clear or atleast free from objectionable tints.

It has heretofore been recognized that in the formation of glass bymelting together such ingredients as silica, lime, soda-ash and saltcake, large volumes of gas, such as carbon dioxide and sulphur dioxideare evolved. There are also present in the glass batch other gases, suchas air and water vapors. Most of these gases escape during melting andsubsequent fining operations, but a few of them become entrapped asminute bubbles in the viscous melt and are very difficult to eliminate.Heretofore it has been customary to subject the glass to so-calledblocking operaherein connotes molten glass in a single recep tions inwhich organic matter, such asblocks of wood, potatoes or the like arethrown into'the gases, which form bubbles of such size that they quicklymake their way to the surface and escape,

rality of receptacles, blended.

tacle, such as-a pot or tank, or in a plurality of such pots or tanks.Therefore, portions, for treatment by the process herein disclosed, maybe taken from a single receptacle or from a pluwhich portions are thenIn practice of the invention a portion of a melt is treated inaccordance with the provisionsof my foregoing invention, first withcarbon'monoxide if desired, in the apparatus disclosed in my patentuntil all orsubstantially all of the melt and there quickly evolve largevolumes of at the sametime carrying away with them many of the smallerbubbles called seed? which would otherwise be permanently retained. Thistype of treatment is not particularly effective in the removal of watervapors, possibly because the latter are actually absorbed in the glass,but when the melt is formed into bodies and allowed partially to coolthe vapors seem to escape to form seed.

In my prior patent, No. 2,274,643, issuing as of the date of March 3,1942, and copending herewith, it is proposed to eliminate water vaporsand other gaseous substances from a glass melt by first bubbling throughthe melt carbon monoxide at appropriate rate. This treatment efiectivelyremoves the gas bubbles including even the d fficulty removable watervapors. treatment is long continued the glass tends to assume a brownishtint which increases in'intensity as the treatment is continued. Asdisclosed in my patent the brown discoloration can be eliminatedbyblowing oxygen or oxygen-containing gas through the melt. Thistreatment however is not always entirely satisfactory, because thetreatment with oxygen tends to pro- In accordance with the provisions ofthe present invention, it is proposed to obviate the foregoingdifliculties, by subjecting only a portion of However, if the gases thattend to form bubbles are removed. The temperatures of treatment may beapproximately within the range of 2000 to 2700 F., de-

pending somewhat upon the melting temperature of the glass. The rate ofhow may be comparatively slow, but should be continued for a considerable period of time, for example; about 1 or 2 hours. This periodmay be extended to 4 or 5 hours, if,desired. As a result'oi thistreatment the glass is freed of seed bubbles of gases and vapors, but isdistinctly discolored." That is it assumes objectionable brownish color.A portion or all of the discolored glass is then treated preferably atabout the same temperature with oxi-- dizing gas. such as air or oxygenuntil it has lost its brownish d scoloration and has assumed a distinctblu sh cast. A portion of the brownish tinted glass is then admixed witha portion of 1 mixture is substantially lost or at least is reduced duce'a'bluish tint in the glass, which sometimes is objectionable.

I to a desired degree. These preparations of course will depend upon.the intensity of the discoloration of the components of the mixture. Itis impossible to define the proportions quantitatively, but in eachinstance it is an easy matter to determine when the necessary admixtureisreached by observation of the color of the mixture. Mixing of the twoglasses in molten state should .be as thorough as possible, in order toobviate streaks in the finished product, which are formed from theglass. This mixing may be performed 10 ing gas.-

material, such as water vapor, carbon dioxide, sulphur dioxide and thelike, which process comprises first bubbling carbon monoxide throughmolten glass containing the gaseous substances as "seed until most ofthe gases, including the water vapor, are removed, then bubbling anoxidizing gas through a portion of the glass, then admixing the latterportion of glass with the portion which has not been treated with theoxidiz- FREDERICK W. ADAMS.

